During the 1970s a major debate erupted among paleontologists. On the basis of new evidence, from the anatomy of the recently-discovered dinosaur Deinonychus to the microscopic bone structure of dinosaurs, paleontologists such as John Ostrom and Bob Bakker proposed that dinosaurs may have been endotherms—animals able to internally regulate their own body temperature. The work generated waves of support and criticism and ultimately gave birth to the image of fast, dynamic dinosaurs that we know today. While things are not as vociferous as they used to be, paleontologists are still investigating what kind of metabolisms dinosaurs had, how they regulated their body temperatures, and other aspects of their physiology. Similar questions have been asked about many of the creatures that lived alongside the dinosaurs, as well, and a new study published last week in Science suggests that some of the great vertebrates that lived in the sea may also have had unique metabolisms which allowed them to carry out active lifestyles.